The present invention relates generally to sensors utilized to detect the quality of fluids, including gas and liquid. The invention also relates to thermal sensors of such fluids, such as fluid flow or property sensors implemented on silicon in microstructure form. The present invention additionally relates to differential pressure sensors utilized in association with flow sensors. The present invention specifically relates to techniques and systems thereof for preventing contamination of such sensors which may come into contact with harsh gases or liquids that can corrode, contaminate with radioactive or live pathogens, freeze-up, overheat, deposit particles or condensate on sensing elements of such sensors.
Flow sensors are utilized in a variety of fluid-sensing applications for detecting the quality of fluids, including gas and liquid. Thermal sensors of such fluids, which detect the fluid flow or property of fluid, can be implemented, for example, as sensors on silicon in microstructure form. For convenience sake, and without limitation, the term xe2x80x9cflow sensorxe2x80x9d will be utilized generically hereinafter for such thermal sensors. The reader will appreciate that such sensors may be also utilized to measure primary properties such as temperature, thermal conductivity, specific heat and other properties; and that the flows may be generated through forced or natural convection.
Generally, a thermal-type flow sensor typically comprises a substrate that includes a heating element and a proximate heat-receiving element or two. If two such sensing elements are used, they are preferably positioned at upstream and downstream sides of the heating element relative to the direction of the fluid (liquid or gas) flow to be measured. When fluid flows along the substrate, it is heated by the heating element at the upstream side and the heat is then transferred non-symmetrically to the heat-receiving elements on either side of the heating element. Since the level of non-symmetry depends on the rate of gas flow, and that non-symmetry can be sensed electronically, such a flow sensor can be used to determine the rate and the cumulative amount of the fluid flow.
Such flow sensors generally face potential degradation problems when exposed to harsh (contaminated, dirty, condensing, etc.) fluids, including gases or liquids that can xe2x80x9cstressxe2x80x9d the sensor via corrosion, radioactive or bacterial contamination, overheating, or freeze-ups. The sensitive measurement of the flow, or pressure (differential or absolute) of xe2x80x9charshxe2x80x9d gases or liquids that can stress corrode, freeze-up, or overheat the sensing elements is a challenge that is either unmet or met at great expense. Among the solutions proposed previously are passivation with the associated desensitization of the sensor, heaters to avoid condensation or freeze-ups (or coolers to prevent overheating) at the expense of sensor signal degradation, cost increase and possible fluid degradation, or filters to remove objectionable particulate matter. Frequent cleaning or replacement of the sensors is an additional, but costly, solution. Sensitive, membrane-based differential pressure sensors can be protected against contamination because no flow is involved, but they are much less sensitive and much more expensive than thermal microsensors, in addition to not being overpressure proof.
The present inventors thus realize that a need exists for a method and system to prevent xe2x80x9cstressingxe2x80x9d flow sensors exposed to harsh fluids or gases. The present invention disclosed herein solves this need through the implementation of a unique purge flow method to counteract corrosive and degrading effects of harsh fluids to which flow sensors are exposed during fluid diagnosis and sensing applications.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is one aspect of the present invention to provide a method and systems for preventing the contamination of sensors and microsensors.
It is another aspect of the present invention to provide methods and systems for preventing the contamination of sensors and microsensors that function in combination with one or more differential pressure sensors.
It is still another aspect of the present invention to provide methods and systems for preventing the contamination of sensors which may come into contact with harsh gases or liquids that can stress (via corrosion, radioactive or bacterial contamination, overheating, freeze-up, deposition of particles or condensation, etc.) of sensing elements of such sensors.
It is yet another aspect of the present invention to provide methods and systems for preventing the contamination of sensors which may come into contact with harsh fluids by providing an imposed purge flow or auxiliary fluid stream in opposition to the flow of the harsh fluid.
The above and other aspects are achieved as is now described. The present invention discloses methods and systems utilizing a purge flow without disturbing flow sensor calibration. Methods and systems are disclosed for preventing contamination of a sensor exposed to a harsh fluid as a result of fluid flow through a bypass channel integrated with a main channel and a restricted portion thereof. The harsh fluid is generally conducted through a main channel and a restricted portion thereof, wherein a portion of the harsh fluid may come into contact with the sensor through the bypass channel. An auxiliary flow of comparatively clean fluid (clean fluid, purge flow, auxiliary fluid or purge fluid may be used interchangeably herein) that is compatible with a composition of the harsh fluid is thus introduced, such that the clean fluid flows past the sensor in opposition to the harsh fluid, thereby preventing the harsh fluid from contacting and degrading the sensor. The auxiliary flow of clean fluid can be configured to comprise an auxiliary purge stream to prevent contamination of the sensor.
The comparatively clean or purge fluid itself may comprise a purge liquid or gas, such as clean, dry air that is compatible with the composition of the harsh fluid. The flow and pressure of the clean fluid can be adjusted utilizing one or more supply regulator valves. The auxiliary flow of clean fluid is generally applied to flow past the sensor in opposition to the harsh fluid, such that the clean fluid flows symmetrically. The sensor itself preferably is composed of one or more thermal microsensors or one or more differential pressure microsensors. Thus, by introducing an auxiliary flow of clean fluid compatible with the composition of the harsh fluid, such that the clean fluid flows past the sensor in opposition to the harsh fluid, the harsh fluid can be prevented from contacting and degrading the sensor through corrosion, radioactive or bacterial contamination, overheating, freeze-up, particle deposition or condensation thereof, or other manners in which the sensor operation is impeded.
The present invention discloses a number of novel features for preventing contamination of sensors exposed to harsh fluids. The use of an auxiliary purge stream to prevent contamination of sensitive flow sensors through corrosion, radioactive or bacterial contamination, overheating, freeze-up, condensation, and particulate matter deposition is a primary feature of the present invention. The use of a symmetric purge stream on two legs of a bypass flow sensor so that that the sensor is able to respond to by-directional flow is also a feature of the present invention. The present invention also discloses the ability to convert an unidirectional sensor to a bi-directional sensor by adding a non-symmetrical flow bias to its ports. Additionally, the use of an auxiliary purge stream to prevent contamination of sensitive flow-based differential sensors is also disclosed herein. The present invention also features the use of an auxiliary purge stream to enable the sensitive measurement of small changes in absolute pressure (differential pressures can be sensed as well), in addition to preventing contamination of the sensitive flow sensor.